This invention relates to new mechanical pencil constructions wherein the lead is advanced by utilizing the natural gripping force applied during writing by the operator's fingers.
In mechanical pencils wherein the lead is advanced by screwing the pencil axis, it is necessary to use both of the operator's hands, the advancement length is not constant, and thin leads may easily be broken if advanced too far.
In pencils wherein the lead is advanced by repeatedly depressing or thumb pumping the upper or eraser end of the pencil, the advancement length is constant and is accomplished by only one hand of the operator. In such pencils, however, it is necessary to vary the hand position in order to pump the upper end of the pencil.
In a pencil wherein a strip plate is provided in a middle portion of the pencil and the lead is advanced by finger pumping, one finger must depress the strip plate while the other fingers of the same hand support the pencil. This is an unnatural or difficult manipulation for the operator. See, for example, Japanese Utility Model Publication No. 51-17938.
There is also a known mechanical pencil in which the pencil axis is bent to advance the lead, but unnatural force application is also required in such a pencil. See, for example, Japanese Utility Model Publication No. 53-2034.
Further, pencils are known wherein the writing end is pumped against the paper or the like to advance the lead. This requires a hard support surface beneath paper, however, and the paper is easily punctured, torn or dotted.